Investigate the hypothesis that a sodium dependent transport carrier is responsible for synaptic GABA release in the goldfish outer plexiform layer (OPL). The control of this release exerted by synaptic input from red cones and dopaminergic interplexiform cells also will be studied. Techniques include biochemical assays of 3H-GABA efflux from living superfused retina and quantitative light microscopic autoradiographic (LM-ARG) analysis of the distribution of H-GABA labeling under a variety of conditions designed to activate and inhibit 3H-GABA efflux. Determine the synaptic circuitry of GABAergic neurons in the goldfish inner plexiform layer. Tissue will be double labeled by immunohistochemistry to identify specific neurons, and with radio amino acids the radioligands in order to identify probable synaptic inputs to the labeled neurons. Techniques include serial reconstruction at the electron microscopic (EM) level and quantitative EM-ARG. The objective is to specify for an identified GABAergic neuron, the distribution of its synaptic contacts and the relative distribution of cholinergic, dopaminergic, and glycinergic synaptic inputs. The long term objective is to understand the transfer of information between retinal neurons. This project should provide much information on the mechanism for the release of neurotransmitters by retinal horizontal cells in all vertebrate species and provide some insight regarding the non-vesicular release of transmitter in other nervous tissues as well. Also, the correlation of identified cells with the distribution of their synaptic inputs when integrated with electrophysiological data, will lead to an understanding of visual encoding and the circuitry by which it is accomplished. Finally, this project will result in new information regarding the coexistence of neuropeptides and neurotransmitters in single retinal neurons, and hopefully provide clues regarding the role of neuropeptides in visual encoding.